serial: sc16is7xx: Put IOControl register into regmap_volatile

Hi, the following patch:

77a82cebf0eb serial: sc16is7xx: Put IOControl register into regmap_volatile

Was introduced in kernel 6.5.

Without it, the debugfs register display can be incorrect for this register.

I would like it to be applied to the stable kernel 6.1.

It applies cleanly and was tested on this kernel using a custom board with a Variscite IMX8MN NANO SOM, a NewHaven LCD, and two SC16IS752 on a SPI bus.

Thank you, Hugo Villeneuve